The car feels like it runs smoother and pulls harder with E. I am well aware of the difference in energy between gasoline and E, I wanted to try E for a while simply because the car is flex fuel capable and I want to log the differences between the two on my car.

The advantage of running ethanol is not very good, it theoretically has a higher octane rating than standard pump gasoline in a pure form, and when blended in is more like mid grade or premium in terms of anti knock index, however it costs a lot more per mile to run and doesn't travel as far as 87 octane, and 91-93 octane fuel probably runs just as smoothly without the loss in fuel economy.

I wanted the flex fuel compatibility in case they push through the E15 or higher as mandatory like the EPA was pushing for, as well as to be able to run on any E blended fuel if necessary, but the owners guide does warn against constantly switching back and forth between fuels.

Of course the choice is up to you as to believe that it would cause harm or not, but the ethanol is corrosive and can knock crud loose in the fuel system. On a new car that's not as much of a concern yet.